On many belt conveyors, and particularly on treadmills, it is necessary to maintain accurate control over the speed of the conveyor. Numerous electronic devices are available for controlling the speed of the electric motor which powers the conveyor belt. Such device typically employ a feedback signal to the motor controller that is proportional to the conveyor belt speed. When the speed of the conveyor belt deviates from its predetermined settings, the motor controller is operative to adjust the speed of the conveyor to bring it back to its predetermined setting.
Photo-optic methods are frequently used to measure the speed of the conveyor. One such method uses a photo-optic disc mounted on the output shaft of the motor. A light emitter is disposed on one side of the disc, and a light detector is disposed on the opposite of the disc. As the motor runs, the photo-optic disc periodically interrupts the transmission of light from the emitter to the detector. The frequency of the resulting on/off signals is fed back to the electronic controller to provide an indication of the conveyor belt speed. In this manner, reasonably accurate speed control can be obtained.
There are several drawbacks with the prior art method of mounting an optical disc on the motor output shaft. Typically, the motor is not directly connected to the conveyor belt pulley, but uses a belt drive arrangement. As the belt drives wear, slippage can occur between the belt and the pulleys. As a result, the indicated speed does not always match the actual speed of the conveyor belt. Additionally, mounting a photo-optic disc on the motor requires additional parts, such as shaft adapters. These additional parts increase the cost of the equipment.